JP2002060943A - Method and device for coating high purity silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce high purity silicon-coated spheres used for solar batteries. SOLUTION: The pressure in the inside of a reaction chamber 122 is reduced, a plasma region 125 is formed by the supply of electric power from a coil 121 in a hydrogen atmosphere containing silicon tetrafluoride, and spherical ceramics, spherical metals or the like 126 charged to the inside of the reaction chamber 122 are scooped up by a scooper 123 according to the rotation of the chamber 122 and are allowed to freely fall 127 into the plasma region 125 to coat and deposit the generated high purity silicon on the surfaces of the spherical ceramics, spherical metal or the like 126 as the objects for covering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for coating an object to be coated with high-purity silicon.

[0002]

2. Description of the Related Art The use of spherical silicon different from the conventional plate-like silicon has been proposed as a new silicon for solar cells. Japanese Patent Application No. 11-510766 (International Publication WO99)
/ 10935) discloses a small-diameter spherical solar battery cell SS (spherical semiconductor device) having a semiconductor core layer or the like on the surface of a spherical core material and a method of manufacturing the same.
The publication also discloses a spherical crystal manufacturing apparatus and the like.

According to the method, a spherical semiconductor device includes a first step of forming a spherical core using a core material made of any one of a semiconductor material, an insulating material, and a metal material; A second step of forming a substantially spherical semiconductor thin film layer on the surface of the core material or in the vicinity of the outside thereof; a third step of forming at least one pn junction in the semiconductor thin film layer; It is stated that it can be formed in a fourth step of forming a pair of connected electrodes.

[0004] The advantage of the spherical shape is that unlike the conventional plate shape, sunlight can be received from any direction, so that the conversion efficiency from sunlight to electricity is three times higher than that of the conventional one. It is considered that spherical silicon can be directly manufactured from the semiconductor device and can be used as it is as a solar cell. Therefore, it is considered that the manufacturing cost can be reduced, for example, the wafer manufacturing process by ingot cutting, which is a conventional process, can be simplified. If the core material of the sphere can be replaced with an inexpensive material, it becomes possible to reduce expensive high-purity semiconductor materials.

[0005] Referring to FIG.
A method for manufacturing a spherical core material 201c by supplying a raw material body 201a of metal-grade silicon to a spherical crystal manufacturing apparatus 200 described in Japanese Unexamined Patent Publication (Kokai) No. H10-209605. In the first preparation stage, the electromagnetic on / off valves 202 to 205 are opened, and the vacuum pump 20 is opened.
6 is activated, and the inside of the drop tube 207 is brought into a predetermined vacuum state. One raw material body 201a is stored in the receiver 208. A preset current is supplied to the infrared heater 209 above the drop tube 207. Next, the electromagnetic floating heating device 210 is energized and the receiving device 208 is turned on.
Of the raw material body 201a
Is dropped, and the raw material body 201a is
By 0, it is heated in a floating state for a predetermined time, and becomes a raw material melt 201b.

Next, when the power supply to the electromagnetic floating heating device 210 is stopped, the raw material melt 201b is dropped into the falling tube 207.
Start to fall in the vacuum of. After the start of the drop, the raw material melt 201b is in a microgravity state.
The spherical shape is obtained by the action of the surface tension b. Next, only the surface of the raw material melt 201b is heated while falling inside the infrared heater 209. Next, while falling below the infrared heater 209, the raw material melt 201b radiates heat by radiant cooling, and solidifies into a true spherical core 201c by the action of the surface tension of the raw material melt 201b. After that, the core 201c that has been solidified at a substantially middle level in the drop tube 207 is
It falls into the silicon oil in the silicon oil tank 212, is stored therein, and is completely cooled.

In this embodiment, metal-grade silicon is used as raw material 2
Although the core material 201c is manufactured as 01a, it is clear that high-purity spherical silicon for solar cells can be produced by using silicon whose purity has been increased to the solar cell grade as a raw material.

Further, the above publication describes a method and structure for manufacturing a spherical solar cell SSA having a metallic core material. FIG. 4 shows an enlarged cross section of a spherical solar cell SSA in which a thin-film silicon solar cell is formed on the surface of the spherical metal core material 2 described in the above-mentioned publication. In FIG. 4, reference numeral 300 denotes a spherical solar cell SSA;
301 is a core material, 302 is an aluminum film, 303 is p
+ Polycrystalline silicon layer, 304 is a polycrystalline silicon layer, 30
5 is an n + polycrystalline silicon layer, 306 is a passivation film, 307 is a surface protection film, 308a is a positive electrode, 308b
Is a negative electrode, and 308c is a junction protective film. In the above publication, an aluminum coating 302 having a thickness of about 100 nm is deposited on the surface of the core material 301, and then an amorphous silicon film (a) having a thickness of about 200 nm is formed on the surface of the aluminum coating 302 as a precursor film. -Si film), silane (Si) is formed by a plasma CVD method.
Although it is stated that H ₄ ) can be deposited while being decomposed to form a non-doped amorphous silicon film, no specific method is described. Furthermore, in the conventional plasma CVD method, it is possible to coat mainly a flat plate, but it is necessary to coat high-purity silicon on an object other than a flat surface such as a sphere and continuously on an industrial scale. Is impossible.

In the method of producing spherical silicon under microgravity, it is necessary to create a microgravity environment and to melt and cool silicon or metal as a raw material during the fall, so that a straight pipe long in the vertical direction is required. Because of the necessity, there are problems such as an increase in equipment scale for mass production.

Further, in order to produce a large amount of spherical silicon or metal serving as a core material in one straight pipe, a large amount of metal for raw material silicon is supplied in the same pipe or continuously supplied molten raw material silicon or metal. Since it is necessary to melt the metal instantaneously and uniformly and to perform cooling while suppressing the adhesion of a large amount of molten silicon or molten metal to each other, the control becomes difficult.

Further, in the above-mentioned publication, the deposition of high-purity silicon on the surface of the core material can be performed on the spherical surface by depositing silane (SiH ₄ ) while decomposing it by a plasma CVD method. The method is not described, and silane (SiH ₄ ) is applied to the surface of a large amount of core material on a practical scale using existing plasma CVD technology and equipment.
It is not possible to deposit and deposit silicon by decomposition.

[0012]

SUMMARY OF THE INVENTION The present inventors have found that when the production process of high-purity spherical silicon is aimed at mass production, the equipment scale becomes large and the control of the production process becomes difficult. In view of the fact that there is no available method for coating high-purity silicon on the surface of a core material that can be used practically, the aim is to create a new manufacturing method and manufacturing equipment that solves these problems. By establishing a simple manufacturing process, a mass-production method and apparatus for easily manufacturing a high-purity spherical silicon coating for a solar cell at low cost is established.

[0013]

According to a first aspect of the present invention, a plasma is generated in a hydrogen (H ₂ ) atmosphere containing silicon tetrafluoride (SiF ₄ ) and / or silane (SiH ₄ ). To decompose silicon tetrafluoride and / or silane, and repeatedly pass the object to be coated through the plasma to deposit silicon generated by decomposition of silicon tetrafluoride and / or silane on the surface of the object to be coated. It is characterized by the following.

According to a second aspect of the present invention, a weir is provided along the axis of rotation on the inner surface of the vessel wall of the substantially cylindrical rotating reaction chamber,
A reaction atmosphere can be controlled by shutting off the inside of the rotary reaction chamber from outside air, and a supply device and a reaction product gas discharge device for silicon tetrafluoride and / or silane and hydrogen, and a device for generating plasma in the rotary reaction chamber The object to be coated is accommodated in the rotating reaction chamber, and the object to be coated carried upward by the weir along with the rotation of the rotating reaction chamber in a plasma region formed in the rotating reaction chamber. Are repeatedly allowed to fall freely to deposit silicon decomposed in the plasma on the surface of the object to be coated.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION According to the method of coating high purity silicon of the present invention, plasma is generated in a hydrogen atmosphere containing silicon tetrafluoride and / or silane, and silicon tetrafluoride and / or silane is generated in the plasma. While being decomposed, the object to be coated as a core material is repeatedly passed through the plasma to deposit silicon generated by decomposition of silicon tetrafluoride and / or silane on the surface of the object to be coated, and to the surface of the object to be coated. It is characterized by being coated with high-purity silicon. For example,
If the object to be coated is a spherical ceramic, a high-purity spherical silicon coating in which the inside of the sphere is made of ceramic can be manufactured.

In the method of coating high-purity silicon of the present invention, since a microgravity environment is not used unlike the production of high-purity spherical silicon disclosed in the above publication, large-scale equipment is not required. Also, for example, when used for solar cells,
Since spherical ceramic, metal, plastic, and the like can be used inside the spherical silicon coating, there is an advantage that expensive high-purity silicon can be effectively used without waste. Further, there is an advantage that the film thickness on the object to be coated can be controlled by repeatedly passing the object to be coated through the plasma.

In the method of coating high-purity silicon according to the present invention, a substantially cylindrical rotating reaction chamber is provided on the inner surface of the chamber along a rotation axis direction, and the reaction atmosphere is controlled by blocking the chamber from outside air. In addition, a device for supplying silicon tetrafluoride and / or silane and hydrogen and a device for discharging reaction product gas are provided, a device for generating plasma is provided in a region in the chamber, and a core to be coated with silicon is provided in the chamber. A material supply device and a discharge device for a silicon coating body are provided, and a coating target carried upward by a weir with the rotation of the chamber is placed in the plasma region in the chamber formed by supplying power to the plasma reaction device. This can be achieved by repeatedly and freely dropping the silicon and uniformly depositing the silicon decomposed in the plasma on the surface to be coated.

In the above apparatus, the plasma is formed near the center of the reaction chamber kept in a reduced pressure atmosphere.
The object to be coated is moved upward along the vessel wall by the weir with the rotation of the chamber, falls freely from above the chamber, and returns to the bottom of the chamber via the plasma in the central region of the chamber. Therefore, the high-purity silicon deposited on the surface of the coating object repeatedly deposits a high-purity silicon layer through the plasma region repeatedly as the chamber rotates, and at a stage where a predetermined deposition amount is reached,
By appropriately tilting the reaction chamber, it is discharged from the other end of the reaction chamber.

(Embodiment) FIG. 1 is a view for explaining a method of coating high-purity silicon according to the present invention, and 100 is a coating apparatus for high-purity silicon. Raw silica sand 101 is charged from a hopper 102 into a reaction tank 103, and hydrogen fluoride (H
F) to form silicon tetrafluoride (SiF ₄ gas). At this time, gasification is promoted by evacuating and evacuation of the reaction tank 103 by the vacuum pump 104. After removing water with a gas cooler 105 and liquefying hydrogen fluoride with a rotary compressor 106, silicon tetrafluoride is added to an expansion tank 107.
Sent to. Another impurity gas such as nitrogen gas is separated in the expansion tank 107 and stored in the surge tank 108.

In the evaporator 109, the gas is heated with hot water or the like to produce silicon tetrafluoride gas.
10 and mixed with the silicon tetrafluoride gas in the silicon tetrafluoride gas cylinder 111 to adjust the pressure. In the plasma reactor 120, the induction heating coil 1 is added to the hydrogen gas supplied from the silicon tetrafluoride gas and the hydrogen gas cylinder 112.
High-frequency power is supplied by 21 to form plasma, and the spherical ceramic supplied from the hopper 113 passes through the plasma region to coat the surface with high-purity silicon. The generated high-purity silicon-coated sphere is discharged from the plasma reactor 120 to the container 114.

When the high-purity silicon-coated sphere has a silicon coating thickness smaller than a desired thickness, the plasma reactor 120 is again supplied from the container 114 through the hopper 113.
Thus, a high-purity silicon-coated sphere having a desired silicon coating thickness can be produced. The gas after the reaction is
The gas is exhausted by the turbo molecular pump 115, passes through the Roots pump 116, liquefies and collects hydrogen fluoride by the gas cooler 117, and is compressed by the rotary compressor 118 to liquefy silicon tetrafluoride. To vaporize and separate hydrogen gas to obtain high-purity silicon tetrafluoride (liquid). The silicon tetrafluoride stored in the expansion tank 119 is sent to the surge tank 108 via the high-pressure line and is reused.

The present invention can be applied not only to a spherical coating but also to a rod or a plate, and its application range is extremely high. Furthermore, high-purity spherical silicon can be used not only for solar cells but also for catalysts and the like.

FIG. 2 is a view showing a cross-sectional structure of a reaction chamber of a coating apparatus for high-purity silicon, wherein 120 is a plasma reactor, 121 is a coil, 122 is a reaction chamber,
Reference numeral 123 denotes a weir, and reference numeral 124 denotes a rotation support ring, and the reaction chamber 122 is rotationally driven by a support roller. In the reaction chamber 122, the high frequency input from the coil 121 turns the depressurized silicon tetrafluoride and a substantially central portion of the hydrogen atmosphere into plasma, thereby generating a plasma region 125. The plasma region 125 is formed near the center of the reactor away from the wall of the reactor as shown in FIG.
It will be about 00-400 ° C. This plasma region 125
Then, silicon tetrafluoride reacts with hydrogen to dissociate silicon according to the following equation (1). SiF ₄ + 2H ₂ → Si + 4HF (1)

A ceramic ball 126 introduced from one end of the reaction chamber 122 is scooped up by a weir 123 formed on the inner surface of the vessel wall with the rotation of the reaction chamber 122, and is carried over the reaction chamber 122.
23 and falls freely in the plasma region 125
The high-purity silicon generated during the step 27 is deposited on the surface, and the surface of the ceramic ball 126 can be coated with the high-purity silicon to a desired thickness.

The reaction process newly devised this time is as follows: high frequency power frequency: 13.56 MHz, input power: 4K
W, gas pressure: 0.1 to 30 Torr, flow rate of raw material gas, silicon tetrafluoride gas: 0.1 to 1 liter / min,
Hydrogen (H2): It can be performed under the conditions of 0.1 to ₂ liter / min.

A spherical ceramic was used as a substrate material for the silicon coating. Note that, in addition to the above, silane may be added as a source gas.

In the above description, silicon tetrafluoride is decomposed with hydrogen (H) radicals using low-temperature plasma to obtain a high-purity silicon coating. It is known that silane is decomposed by thermal plasma CVD to obtain a polycrystalline thin film of silicon at a high speed. In forming a thin film using this thermal plasma, silicon tetrafluoride can be decomposed at high speed by replacing the raw material with silicon tetrafluoride to obtain a polycrystalline thin film of silicon at high speed.

That is, in the above-described embodiment, the production of high-purity silicon-coated spheres by low-temperature plasma has been described. However, high-purity spherical silicon can be obtained in the same manner by changing the plasma source to thermal plasma. The deposition conditions are much easier and require less energy than obtaining a uniform and uniform polycrystalline thin film.

The deposition conditions are basically the same as those for forming a polycrystalline film, and can be implemented, for example, under the following conditions. Gas pressure: 100 to 1000 Torr Electric power: 10 to 50 kW Gas composition and flow rate: Silicon tetrafluoride gas 0.1 to 10 L / min Argon (Ar) 50 to 100 L / min Hydrogen (H ₂ ) 0.1 to 10 L / Min

As is clear from the above description, these reaction processes can be performed in principle with silicon tetrafluoride and silane. The method and apparatus for producing a high-purity silicon-coated sphere described above using silane as a starting material can be similarly performed using silane instead of silicon tetrafluoride, and the basic reaction conditions and the like described above. Does not change. In addition,
The object to be coated can cover a wide range of high-purity silicon, such as metal-grade silicon and plastic, in addition to ceramics. However, considering the durability, etc., the thermal expansion coefficient of the object to be coated and the high-purity silicon that is the coating material Needless to say, it is desirable that they be similar.

[0031]

According to the present invention, when the conventional manufacturing process of high-purity spherical silicon is aimed at mass production, the equipment scale becomes large and the control of the manufacturing process becomes difficult.
Furthermore, the present invention provides a new manufacturing method and a new manufacturing apparatus that solves the problem that there is no practical method of coating a high-purity silicon on the surface of a core material, and a simple manufacturing process that does not use microgravity. Accordingly, it is possible to provide a mass production method and apparatus for easily and at low cost producing a high-purity spherical silicon coating for a solar cell.

[Brief description of the drawings]

FIG. 1 is a view for explaining steps of a high-purity silicon coating method according to the present invention.

FIG. 2 is a diagram for explaining a cross-sectional structure of a reaction chamber of the high-purity silicon coating apparatus according to the present invention.

FIG. 3 is a diagram for explaining an example of a conventional spherical crystal manufacturing apparatus.

FIG. 4 shows a spherical solar cell SS according to a conventional manufacturing method.
It is sectional drawing which shows an example of the structure of A.

[Explanation of symbols]

100: coating apparatus for high-purity silicon, 101: raw silica sand, 102: hopper, 103: reaction tank, 104: vacuum pump, 105: gas cooler, 106: rotary compressor,
107: expansion tank, 108: surge tank, 109 ...
Evaporator, 110: pressure adjusting tank, 111: silicon tetrafluoride gas cylinder, 112: hydrogen gas cylinder, 11
3: hopper, 114: container, 115: turbo molecular pump, 116: roots pump, 117: gas cooler, 1
18 rotary compressor, 119 expansion tank, 120 plasma reactor, 121 coil, 122 reaction chamber, 123 weir, 124 rotary support ring, 125 plasma region, 126 ceramic ball, 127 free fall , 200: spherical crystal production apparatus, 201a: raw material,
201b: raw material melt, 201c: core material, 202 to 205
... Electromagnetic on-off valve, 206 ... Vacuum pump, 207 ... Drop tube, 208 ... Receiver, 209 ... Infrared heater, 210
... Electromagnetic floating heating device, 211 ... Electromagnetic open / close shutter, 2
12: Silicon oil tank, 300: Spherical solar cell S
SA, 301: core material, 302: aluminum film, 30
3 ... p + polycrystalline silicon layer, 304 ... polycrystalline silicon layer, 305 ... n + polycrystalline silicon layer, 306 ... passivation film, 307 ... surface protective film, 308a ... positive electrode,
308b: negative electrode, 308c: junction protective film.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA04 AA06 AA17 BA29 CA05 CA18 FA01 GA08 KA02 KA05 5F045 AA08 AB02 AC01 AC02 DP25 DP27 EM10 5F051 AA03 BA14 CB12 CB29 DA01

Claims (2)

[Claims] 1. A plasma is generated in a hydrogen (H ₂ ) atmosphere containing silicon tetrafluoride (SiF ₄ ) and / or silane (SiH ₄ ), and silicon tetrafluoride and / or silane is decomposed in the plasma. A method for coating high-purity silicon, wherein the object to be coated is repeatedly passed through the plasma to deposit silicon generated by decomposition of silicon tetrafluoride and / or silane on the surface of the object to be coated. . 2. A weir along the direction of the rotation axis is provided on the inner surface of the vessel wall of the substantially cylindrical rotating reaction chamber, and the inside of the rotating reaction chamber is blocked from the outside air so that the reaction atmosphere can be controlled and silicon tetrafluoride can be controlled. And / or a device for supplying silane and hydrogen, a device for discharging reaction product gas, and a device for generating plasma in the rotary reaction chamber are provided, and the object to be coated is accommodated in the rotary reaction chamber and formed in the rotary reaction chamber. The object to be coated, which is carried upward by the weir with the rotation of the rotary reaction chamber, is repeatedly and freely dropped in the plasma region thus deposited, and silicon decomposed in the plasma is deposited on the surface of the object to be coated. A high-purity silicon coating apparatus characterized in that: